Currently, in the technical field of internal combustion engines, the energy used for power output of internal combustion engines only accounts for 35%-45% of the total amount of heat produced by the burning of fuel oil, while that spirited by exhaust gases occupies 30%-40%; therefore, recycling exhaust gas energy from internal combustion engines as much as possible can increase the output work of internal combustion engines, raise the thermal efficiency of internal combustion engines and improve fuel consumption, and is energy-saving and environment-friendly. The invention with the Chinese patent application No. CN104329148A and the application publication data of Feb. 4, 2015 discloses a two-stage power turbine system, including an internal combustion engine body, an intake manifold, an exhaust manifold, a turbocharger, a low-pressure power turbine, a high-pressure power turbine and a mechanical driving device, wherein the turbocharger includes a charging turbine and an air compressor; an inlet of the charging turbine is connected with the exhaust manifold, and an outlet of the charging turbine is connected with an inlet of the low-pressure power turbine; the high-pressure power turbine and the low-pressure power turbine are coaxially connected; an inlet of the high-pressure power turbine is connected with the exhaust manifold through a bypass pipeline, and after being connected parallelly with an outlet of the low-pressure power turbine, an outlet of the high-pressure power turbine is connected with the exhaust manifold. Although the invention can increase the recycling rate of exhaust gas energy from internal combustion engines and improve the output power of internal combustion engines, the invention still has the following defects: in the invention, the high-pressure power turbine and the low-pressure power turbine are coaxially connected, and when intake pressure falls short for a demand set by an internal combustion engine, the low-pressure power turbine is required to operate to drive the high-pressure power turbine to operate so that the exhaust gas energy from the internal combustion engine is transferred to a crankshaft of the internal combustion engine through the mechanical driving device, which causes the recycling rate of exhaust gas energy from the internal combustion engine to be relatively low.